This invention relates generally to improvements in devices and related installation procedures for surgical implantation of ligament grafts, such as a ligament graft used in the reconstruction of the anterior cruciate ligament of the human knee. The invention provides improved femoral and tibial fixation units attached to opposite ends of a ligament graft and adapted to seat firmly and securely against cortical bone. The invention further provides means for variably and selectively adjusting the tension applied to the implanted ligament graft.
Ligament grafts have been increasingly used in surgical reconstruction of human joints, particularly with respect to surgical knee reconstruction. As one common example, reconstruction of the anterior cruciate ligament may entail removal of a damaged natural ligament and replacement thereof by a ligament graft such as autogenous hamstring graft tendons harvested from the patient. In a typical procedure, a pair of generally aligned and relatively small tunnels are formed in the adjoining ends of the femoral and tibial bones at locations near the normal attachment sites of the natural anterior cruciate ligament. The ligament graft is positioned with its opposite ends extending into and/or through these femoral and tibial tunnels, and thereat fastened to the patient bone. A wide variety of different fastening structures and related methods have been proposed, such as the use of bone screws, bone staples, and the like, many of which involve anchoring of one or both ends of the ligament graft to relatively soft cancellous bone material. Other fastening devices and methods have looped the ends of the ligament graft through sutures which are in turn attached to patient bone.
Pre-existing systems and methods for anchoring the ligament graft have exhibited a number of disadvantages and potential failure modes. More specifically, anchoring of the ligament graft to relatively soft cancellous bone may permit the mounting structure to work loose over time, particularly when subjected to large physiologic loads associated with strenuous physical activity. The use of sutures to support one or both ends of the ligament graft provides a relatively unstable connection which can stretch or creep over time to provide a nonrigid fixation point. In addition, prior ligament graft attachment methods have not adequately restrained the ligament in a substantially centered position within the bone tunnels, without side-to-side sway motion or twisting, resulting in potential widening of the bone tunnels. Such tunnel widening abrades and wears the ligament graft and can result in undesirable loosening of the ligament graft. Additionally, conventionally available systems have not allowed equal distribution of force applied to the fibers of the ligament graft. Lastly, prior anchoring systems and methods have generally not provided a simple yet easily manipulated mechanism for variably and closely selecting the tension force applied to the implanted ligament graft.
The present invention provides an improved ligament graft placement and anchoring system which overcomes these problems and disadvantages by structurally supporting the ligament graft from relatively hard cortical bone, while additionally providing a simple and easily adjustable mechanism for variably selecting the tension force applied to the ligament graft, prior to completion of the surgery.
In accordance with the invention, a ligament graft system and method are provided for securely anchoring a ligament graft to patient bone, wherein the ligament graft is supported in a secure and stable manner from cortical bone, and further wherein means are provided for closely and variably selecting the tension applied to the ligament graft. The graft system and method are designed principally for use with autogenous hamstring graft tendons utilized for ligament replacement such as arthroscopic aided reconstruction of the anterior cruciate ligament of the human knee, although it will be recognized and understood that the invention can be expanded to applications with other types of grafts and other joint reconstruction procedures.
In general terms, an elongated ligament graft is assembled between femoral and tibial fixation units, and the thus-assembled system is fitted into and through generally aligned tibial and femoral tunnels formed in patient bone. A pivotally mounted anchor pin at a leading or upper end of the femoral fixation unit is adapted for positional shifting upon emergence from the femoral tunnel to overlie and seat securely upon cortical bone. In one preferred form, a winged washer at a trailing or lower end of the tibial fixation unit is adapted to engage and seat securely against cortical bone. A set nut or lock nut adjacent to the winged washer is positioned to retain the winged washer, and also to variably select the tension applied to the ligament graft.
More particularly, in one preferred form of the invention, the elongated ligament graft is looped through an open stirrup formed at the trailing end of an elongated stirrup rod comprising a portion of the femoral fixation unit. The anchor pin has a generally bullet-shaped configuration and is mounted pivotally at a leading end of the stirrup rod. The free ends of the ligament graft trail from the stirrup and are threaded and captured between a wedge-shaped bolt head seated within a capture cylinder comprising a portion of the tibial fixation unit. An elongated threaded tibial adjustment bolt projects downwardly in a trailing direction from the bolt head and carries the low profile winged washer and associated set nut.
These system components are assembled prior to patient placement and are slidably fitted into and through the generally aligned and preformed tibial and femoral tunnels formed in patient bone, with the bullet-shaped anchor pin pivoted to a position generally in-line with the stirrup rod. In the preferred form, at least one suture may be attached to the anchor pin and threaded through the tibial and femoral tunnels, wherein this suture may be accessed and used to assist in pulling the system components into the bone tunnels. Upon emergence of the anchor pin from the femoral tunnel, the anchor pin is pivotally shifted to overlie and seat securely upon cortical bone at the upper end of the femoral tunnel. The tibial fixation unit is then drawn downwardly to apply a selected tension to the ligament graft, and the winged washer and associated set nut are suitably advanced on the threaded adjustment bolt to bear against cortical bone at the lower end of the tibial tunnel. Set or lock nuts are provided on the adjustment bolt to retain the graft capture cylinder and the winged washer thereon in the desired set positions. In addition, the winged washer desirably includes an anti-backout tab which can be bent or deformed by the surgeon to engage the associated set nut in a manner locking the wing nut against back-out rotation.
In an alternative preferred form, a modified tibial fixation unit includes the elongated tibial adjustment bolt which projects downwardly from the bolt head and associated graft capture cylinder has a plurality of enlarged surface elements such as hemispherically shaped elements formed along the length thereof. The adjustment bolt is adapted to be engaged and drawn downwardly by means of a suitable tensioning tool to apply a selected tension to the ligament graft. In the desired tensioned position, a lock clip is fitted onto the adjustment bolt to engage a selected one of the enlarged surface elements, wherein this lock clip is sized and shaped for relatively low profile bearing and seating against cortical patient bone at the lower end of the tibial tunnel.
Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.